Use of a multilayer film in a high-speed pouch forming, sealing and filling machine, and method of operation

ABSTRACT

The multi-layer film structure having an inner sealing layer ( 36 ) which comprises metallocene resin, a core ( 38 ) which includes polypropylene copolymer and an outer layer ( 37 ) and wherein the multi-layer film structure has a thickness (X) within a range between about 50 and 70 microns (2.0-2.75 mil). By utilizing this thin film with specific properties the sealers may be operated at lower temperatures thereby resulting in an energy saving and they produce seals having improved seal strength of 30% to 50% as compared with known prior mono-layer polyethylene film. The seal initiation temperature is reduced by 10° C. to 15° C. and the film exhibits an improved machine direction tensile strength of 25% to 40% and an improvement of 30% to 50% in puncture resistance as compared with a 76 microns (3 mil) mono-layer polyethylene film. This results in a reduction in the sealing cycle time and an increase in the throughput of the machine. This results in a liquid pouch having a substantial improvement in drop test performance, puncture resistance and seal strength. The machine accomplishes better seals with less energy, requires less downtime for roll changes and maintenance and increase throughput.

TECHNICAL FIELD

The present invention relates to a high-speed pouch forming, filling andsealing machine and method of operation using a multi-layer filmstructure that can be used for packaging consumable liquid products,such as flowable dairy products, fluid milk, sour cream, yoghurt, fruitjuices, water, in flexible plastic pouches.

BACKGROUND OF THE INVENTION

Traditionally, in North America, the film used for packaging fluid milkor the like in flexible plastic pouches consists of a 76 microns (3 mil)mono-layer polyethylene film.

However, this standard film has some disadvantages which should beovercome. For example, the packaging operation requires a certain amountof electrical energy for the heat sealing operation due to the thicknessof the film. To generate this heat, electrical energy is dispensed. Itis desirable to develop a process that could generate the energyconsumption in order to make the operation more economically feasible.Another problem involved with the sealing operation is that some of thehardware, such as the sealing element per se and the rubber and Teflon™parts associated with the sealing jaws have a relatively short usefullife, requiring frequent changes and again increasing the cost ofproducing milk pouches.

Yet another problem resulting from the packaging of liquids with amono-layer polyethylene film is the amount of waste and machine downtimedue to film roll changes and seal breaks. Packaging milk or otherliquids with mono-layer polyethylene also involves the use of a narrowsealing window which renders the operation somewhat difficult. Finally,the seals obtained with this type of film pouches, often exhibitsweaknesses that can cause fluid leakage.

Polymer film pouches made from a polyethylene film structure and usedfor packaging flowable materials such as milk, are known and examples ofsuch are described in U.S. Pat. Nos. 5,288,531; 5,360,648; 5,364,486 and5,508,051, all of which have issued to the Dow Chemical Company.

U.S. Pat. No. 5,972,443 discloses a multi-layer film comprising a layerof high density polyethylene (HDPE) as the stiffening layer, and a layerof copolymer of ethylene/C₄-C₁₀ α-olefin, also referred to as ametallocene resin. An important disadvantage with HDPE is that althoughit has a high density, by the industry standards, its rigidity is suchthat a great amount thereof must be used to reach an acceptable level.

U.S. Pat. No. 5,849,127 describes a multi-layer film comprising at least3 layers, i.e., a first layer made of a metallocene resin (orethylene/α-olefin copolymer); a second layer made of a polyolefin; and athird layer made of a second metallocene resin, the second layer beingchemically different from the first and third layer, and sandwichedtherebetween.

WO 9414609 describes a multi-layer coextruded film comprising two outerlayers of a metallocene resin (referred to as linear low densitypolyethylene), and an intermediate layer of a blend of linear lowdensity polyethylene and a polyolefin selected from the group consistingof homopolymers of propylene, copolymers of propylene and ethylene, andmixtures thereof.

It would therefore be highly desirable to develop a multi-layer filmcomprising a stiffening layer having improved properties. For example,if the material of the stiffening layer had a lower density combinedwith a higher rigidity, this would allow a higher yield than with HDPEfor a given rigidity requirement.

SUMMARY OF INVENTION

It is a feature of the present invention to provide a thinnermulti-layer coextruded film structure, which overcomes some or all ofthe disadvantages of the prior art and incorporated in a pouch forming,filling and sealing machine to improve on its method of operation andthroughput.

It is another feature of the present invention to provide fluidcontaining pouches that exhibit desirable properties as compared to thepouches of the prior art. These pouches are made of a multi-layer filmstructure according to the invention that improves horizontal sealstrength, exhibits lower horizontal seal thinning, and minimizes postconsumer waste. The pouches therefore have a higher stiffness enablingpouring of liquid, and exhibit a substantial improvement in drop testperformance and puncture resistance.

It is another feature of the invention to provide a multi-layer filmstructure which makes it possible to reduce the material used ascompared to the films of the prior art, thereby providing a higheryield.

It is another feature of the present invention to provide a multi-layerfilm structure for packaging liquid that can be sealed at much lowerseal initiation temperature and has greater machine direction tensilestrength.

It is another feature of the present invention to provide a multi-layerfilm structure for packaging liquid into pouches, which ensures areduction of the electrical energy required for sealing due to lowerheat initiation temperature and lower mass to be sealed.

It is another feature of the present invention to provide a multi-layerfilm structure for packaging consumable liquid products into poucheswhich uses lower sealing temperature and thereby improves the usefullife of the jaw sealers, such as the rubber, and electrical sealingheads, and resulting in overall energy reduction.

It is another feature of the present invention to provide a multi-layerfilm structure for packaging liquid wherein sealing is easier to operatedue to a wider sealing window, and speed increase is made possible as aresult of a faster sealing cycle.

According to another feature of the present invention there is provideda high-speed pouch forming, filling and sealing machine and its methodof operation and utilizing sealing heads which operate at lowertemperatures due to a decrease in the film thickness as compared with 76microns (3 mil) mono-layer polyethylene film and thereby resulting in anelectrical energy saving and wherein the thin film permits the machineto obtain a substantially higher yield with a film roll substantiallythe same size as with the 76 μm (3 mil) film.

According to the above features, from a broad aspect, the presentinvention provides a multi-layer structure for use in packagingconsumable liquid into flexible pouches comprising an inner sealinglayer, an outer layer, and a core comprising one or more layerssandwiched between said sealing layer and said outer layer, wherein

the sealing layer comprises about 40% to 100% weight percent of apolyethylene/α-olefin copolymer, also known as a metallocene resin,having a density of between about 0.902 and 0.912, and about 0 to 60weight percent of a polyolefin, preferably low density polyethylene, ora mixture of at least 2 polyolefins, preferably low densitypolyethylene, linear low density polyethylene.

the outer layer comprises a polyolefin, preferably low densitypolyethylene, or a mixture of at least 2 polyolefins, preferably lowdensity polyethylene, linear low density polyethylene or very low lineardensity polyethylene,

the core comprising at least one layer made of a mixture of about 20 to90 weight percent of a polypropylene homopolymer, copolymer orterpolymer, and about 10 to 80 weight percent of a polyolefin,preferably low density polyethylene, or a mixture of at least 2polyolefins, preferably low density polyethylene and linear low densitypolyethylene,

said multi-layer structure having a thickness within a range betweenabout 50 and 70 μm (2.0-2.75 mil).

The use of polypropylene homopolymer, copolymer or terpolymer in thecore (or stiffening layer) is particularly advantageous for severalreasons. It has a melting point higher than HDPE, thereby allowing ahigher viscous strength during the sealing process because polypropylenesolidifies at a higher temperature. It also has a rigidity significantlyhigher and a density lower than those of HDPE. As a result, because thedensity is lower, the yield is higher.

According to a still further broad aspect of the present invention thereis provided a high-speed pouch forming, filling and sealing machinewhich comprises means to draw a multi-layer film from a film roll over apouch-former to form a plastic film tube having an overlap vertical filmedge. A vertical sealer is provided and has a sealing head for heatfusing the overlap vertical film edge form a vertical seal. A fillertube extends into the plastic film tube for injecting a consumableliquid product at a filling location of the plastic film tube. Ahorizontal sealing jaw, having an electrical thermal sealing element, isprovided for effecting a horizontal seal across the plastic film tubeand spaced below the filling location and for simultaneously severingthe tube to form a top transverse seal for a filled pouch and a bottomtransverse seal for a pouch being filled. The multi-layer film has aninner sealing layer, an outer layer and a core sandwiched therebetween.The characteristics of this film are described above. The horizontal andvertical seals have an improved seal strength of 30% to 50% as comparedwith the 76 μm (3 mil) mono-layer polyethylene film and a 10° C. to 15°C. reduction in seal initiation temperature, an improved machinedirection tensile strength of 25% to 40% and an improvement of 30% to50% in puncture resistance, while reducing the sealing cycle time andincreasing the throughput of the machine.

According to a still further broad aspect of the present invention thereis provided a method of forming, filling and sealing a pouch with aconsumable liquid at high-speed. The method comprises the steps ofproviding, in roll form, a multi-layer film sheet having an innersealing layer, an outer layer and a core sandwiched therebetween, asdescribed above. The film sheet is drawn, by drawing means over apouch-former to form a plastic film tube having an overlap vertical filmedge. The overlapped vertical film edge is sealed by a vertical sealerto form a vertical seal. A horizontal seal is formed across the plasticfilm tube by a horizontal sealing jaw positioned at a predeterminedlocation below the vertical sealer. Simultaneously as the horizontalseal is made, the horizontal sealing jaw severs the tube and forms a tophorizontal seal for a filled film pouch and a bottom horizontal seal fora pouch being formed and filled. The horizontal and vertical seals havean improved seal strength of 30% to 50% as compared with a 76 μm (3 mil)mono-layer polyethylene film and a 10° C. to 15° C. reduction in sealinitiation temperature and an improved machine direction tensilestrength of 25 to 40%, while reducing the sealing cycle time. Aconsumable liquid is continuously fed within the plastic film tube belowthe vertical sealer and above the horizontal sealing jaw at a fillinglocation.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram illustrating basic component parts of theimproved high-speed pouch forming, sealing and filling machine of thepresent invention;

FIG. 2a is an enlarged fragmented and partly sectioned view showing thehorizontal sealing jaws of a prior art machine and the defect of sealthinning that occurs when using conventional 76 microns (3 mil)mono-layer polyethylene film;

FIG. 2b is an enlarged sectional view of the horizontal seal of thepouch illustrated in FIG. 2a which better illustrates seal thinning;

FIG. 3 is a sectional view illustrating the multi-layer film of thepresent invention which comprises 3 layers; and

FIG. 4 is an enlarged fragmented sectional view showing a top horizontalseal formed on a pouch and using a three-layer film of the presentinvention and wherein film thinning is eliminated.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the present application, the term “polyolefin” refers to anypolymerized olefin, which can be linear, branched, cyclic, aromatic,aliphatic, substituted or unsubstituted.

Further, the phrase “ethylene/α-olefin” refers to heterogeneousmaterials as linear low density polyethylene (LLDPE) and very low andultra-low density polyethylene (VLDPE and ULDPE); and homogeneouspolymers such as metallocene catalyzed polymers. These materials arewell known to anyone of ordinary skill in the art and include copolymersof ethylene with one or more comonomers selected from C₄-C₁₀ α-olefins,like 1-butene, 1-hexene, 1-octene, in which the molecules of thecopolymers comprise long chains with relatively few side chain branchesor cross-linked structures. This molecular structure is to be contrastedwith conventional low or medium density polyethylenes which are mosthighly branched than their respective counterparts. Examples of suitablecommercial ethylene/α-olefin copolymers include Exact™ and Exceed™(Exxon), Tafmer™ (Mitsui Petrochemical) and Affinity™ (Dow Chemicals).

Referring now to the drawings and more particularly to FIG. 1 there isshown generally at 10 basic component parts of a high-speed pouchforming, filling and sealing machine constructed in accordance with thepresent invention. These basic component parts are only schematicallyillustrated and are well known in the art. The improvement in themachine resides primarily in the vertical sealer operatingcharacteristics and the horizontal sealing jaws characteristics, as willbe described later. The sealers are controlled to operate with a newmulti-layer film whereby to increase the throughput of the machine andprovide filled pouches having improved strength and wherein the sealsare greatly improved over those of the prior art, thereby resulting in amachine which can output more filled pouches, achieve a significantwaste reduction and less downtime as compared with prior art machinesusing a 76 microns (3 mil) mono-layer polyethylene film. As hereinshownthe high-speed pouch forming, sealing and filling machine comprises afilm roll 11 provided with a multi-layer film 12 which is guided throughguide rolls and tensor rolls 13 to a top end of a pouch former 14 wherethe plastic film is guided and folded to form a plastic film tube 15having an overlap vertical film edge 16. A filter tube 17 extends withinthe pouch former 14 and the tube 15 and has a liquid discharge end 17′positioned at a filling location 18.

A vertical sealer 19 has a sealing head 20 provided with a heatingelement 21 and a backing member 22 is disposed vertically aligned behindthe overlap vertical film edge 16. A vertical seal is formed by fusingthe overlapped edge 16 along the plastic tube 15 above the fillinglocation 18. A horizontal sealing jaw assembly 23 is provided spaced ata predetermined distance below the filling location 18 whereby to form ahorizontal seal across the film tube 18 and at the same time sever thetube to form a sealed pouch 24 filled with a consumable liquid 25therein. The pouch is then released on a discharge conveyor means 26.

The horizontal sealing jaw assembly 23 is comprised of a sealing head 27provided with an electrical impulse sealing wire element 28 to sever thefilm tube as well as to form a top horizontal seal 29 for the pouch 24and a bottom horizontal seal 30 for the next pouch being formed hereinillustrated by reference numeral 24′. The horizontal sealing jawassembly 23 also has a backing member 31 which is provided as a rubberor Teflon™ pad 32 to serve as a backing for the electrical impulsesealing wire element 27. From time-to-time it is necessary to change thepad and the wire element as they wear down. By operating at lowertemperature, 10° C.-15° C. lower than the prior art discussed above,these elements have a longer life cycle and there is less machinestoppages. The jaw assembly 23 may move in and out in unison to form theseal or the backing member 31 may be stationary and positioned close tothe film with only the sealing head 26 moving in and out. Other suitablesealing assemblies are conceivable provided they can achieve the sameresults. The film sheet 12 is drawn in continuous motion by a pair ofdraw rolls 33 in a manner well known to the art. So far we have decidedthe basic component parts of a well known pouch forming, sealing andfilling machine such as the Thimonnier M3200™ or a Prepak IS-7™.

The present invention resides in the provision of a novel multi-layerfilm structure in combination with the machine to enhance theperformance of the machine. This enhancement is achieved by controllingthe temperature of the sealing assemblies 19 and 23 wherein they operateat temperatures that are lower than prior art machines. The draw rolls33 are also operated at higher speeds whereby to increase the throughputof the machine while producing horizontal seals which are much superiorthan the above-mentioned prior art machines and resulting in aproduction having less post consumer waste and permitting the machine tooperate with less downtime previously caused by malfunction or plasticfilm roll change.

In particular the high-speed pouch forming, sealing and filling machineas above described is utilized for the production of milk pouches andsuch machines conventionally use a 76 microns (3 mil) mono-layerpolyethylene film which heretofore was the best film product availablefor this use. FIGS. 2a and 2 b illustrate one of the more seriousproblems that these machines have been plagued with in the production ofsuch pouches and namely the formation of seal thinning. As shown in FIG.2a the pouch 24 has just been formed with the horizontal seal 29 severedand the filled pouch 24 is being discharged under the influence of itsown weight. As the seal is formed the weight of the liquid 25 within thepouch 24 exerts a load on the horizontal seal and this causes sealthinning in the regions 35. Seal thinning is caused by the stretching ofthe polyethylene in the area of the seal which causes the film to thinout in this region. FIG. 2b better illustrates the seal thinning area 35and as herein shown, this produces a weakness in the pouch 24 in thisthinner stretched area of the seal. As the pouch is dropped on thedischarge conveyor 26, it is subject to impact, which could burst thefilm in the seal thin region 35. Furthermore, as these pouches arehandled by consumers or during packaging, pressures applied against theliquid 25 within the pouch exerts a force on the thin film region 35,which again could cause leakage. Weak seals caused by seal thinning haslong existed and no adequate solution has been found to date to improvethese machines and the film in order to substantially overcome theabove-mentioned problems. We have now discovered that by producing afilm which can substantially eliminate seal thinning and improve onmachine performance that a superior pouch can be produced at a highermachine throughput and at a lower cost by substantially eliminating theabove production problems.

In a preferred embodiment the multi-layer film of the present inventionis a three-layer film as schematically illustrated in FIG. 3. Thethree-layer film has an inner sealing layer 36, an outer layer 37 and acore layer 38 sandwiched therebetween. The core may be of one or severallayers of polymers. Seal thinning is substantially eliminated by thecombination of the metallocene sealing layer and a core incorporating ahigher melting point high impact polypropylene. Example of a suitablepolypropylene for the purposes of the present invention comprisesPro-Fax™, manufactured and sold by Montell.

According to preferred embodiments, the sealing layer 36 representsabout 10 to 30 weight percent of the structure, the core 38 representsabout 30 to 70 weight percent of the structure, and the outer layer 37represents about 10 to 30 weight percent of the structure.

Preferably, the sealing layer 36 is a metallocene resin having a densitywithin a range between about 0.905 and 0.912, and the thickness “x” ofthe multi-layer structure is preferably about 65 μm.

In accordance with another embodiment, the multi-layer structure has aninner layer 36 having a seal initiation temperature between about 80 and95° C.

The sealing layer preferably comprises between about 70 and 95 weightpercent metallocene polyethylene, more specifically between about 75 and85 weight percent.

The preferred copolymer to be used in the core 38 consists of highimpact polypropylene copolymer having a melting point differential withthe metallocene sealing layer of at least 40° C. This particular aspectof the present invention represents a most preferred embodiment.

The invention also relates to a process for preparing the multi-layerstructure by providing a sealing composition comprising about 40 to 100weight percent of an ethylene/α-olefin copolymer, or metallocene resin,having a density between about 0.902 and 0.912, and about 0 to 60 weightpercent of a polyolefin or a mixture of at least 2 polyolefins, an outerlayer composition comprising a polyolefin or a mixture of at least 2polyolefins, and a core composition comprising a mixture of about 20 to90 weight percent of a polypropylene homopolymer, copolymer orterpolymer and about 10 to 80 weight percent of a polyolefin or amixture of at least 2 polyolefins, simultaneously co-extruding in ablown or cast coextrusion line, the sealing layer composition, the outerlayer composition and the core composition, and feeding the co-extrudedcompositions to a die under conditions to provide a thickness betweenabout 50 and 70 μm.

When compared to the traditional 76 μm (3 mil) mono-layer polyethylenefilm, the advantages of the film according to the invention when used invertical form, fill & seal machine, such as shown in FIG. 1, for aliquid pouch application are as follows:

Film:

about 20% improvement in yield (sq.inch per lbs)

a 10° C. to 15° C. lower seal initiation temperature

25% to 40% greater machine direction tensile strength (psi)

30% to 50% improvement in puncture resistance (lbs/mil)

Pouch:

a 30% to 50% improvement in horizontal seal strength (lbs/inch)

a reduction of horizontal seal thinning from more than 20% to less than3% (typical seal thinning is greater than 20% for mono-layer films inthis application)

about 20% post consumer waste reduction

an improvement of 30% to 50% in stiffness, (% modulus in psi) whichenables pouring of liquid at a lower gauge

a two to threefold improvement in drop test performance.

Pouch filling and sealing application

a 20% to 40% reduction of energy required for sealing due to the lowerheat initiation temperature and the lower mass (33% less) to sealthrough an improvement in the useful life of consumable itemsproportional to the energy reduction (rubber, Teflon™, sealing element)

about 20% reduction of wastes and downtime caused by film roll changes

easier operation due to a wider sealing window

increased speed made possibly by a faster sealing cycle

FIG. 4 illustrates the improvement in the seal of the pouch 24″ achievedwith the multi-layer film of the present invention. As can be seen sealthinning below the top horizontal seal 29′ is eliminated and results ina pouch which is free of seal defects and which exhibits all of theabove listed advantages of the pouch as well as the machines. Althoughthe multi-layer film of the present invention has been described withparticular reference to a pouch forming sealing and thinning machinesuch as a VFFS machine like a Thimonnier M3200™ or Prepak IS-7™, it isconceivable that this film may have other uses and the present inventionis not intended to limit the scope of its use in such machines.

The invention will now be illustrated by means of the following tablewhich is not intended to limit the scope of the invention as defined inthe appended claims.

DG 2 DG 10 Comp 1 Comp 2 Thickness (mil) 2.5 2.5 3.0 3.0 Film Yield12,200 12,200 10,200 10,200 Seal Initiation Temperature (° C.) 80 80 9595 Puncture (peak load in lbs) 22 22 17 16 Horizontal Seal Strength(lbs/inch) 9.4 9.1 7.0 6.8 Seal Thinning 2.1% 3.0% >20% >20% Stiffness(1% Modulus in lbs) 170 170 100 103 Glopak Drop Test (# of times) 7-97-9 2-4 2-4

The above are typical values obtained from representative samples, DG 2and DG 10 are Glopak experimental multi-layer films. Comp 1 and Comp 2are competitive mono-layer films used in Canadian dairies.

What is claimed is:
 1. A method for producing flowable materialcontaining pouches, said method comprising: producing said pouches in ahigh-speed pouch forming, filling and sealing machine comprising meansto draw the multi-layer film from a film roll over a pouch former toform a plastic film tube having an overlapped vertical film edge, avertical sealer having a sealing head for heat fusing said overlappedvertical film edge to form a vertical seal, a filler tube extending intosaid plastic film tube for injecting a flowable material product at afilling location of said plastic film tube, a horizontal sealing jawhaving an electrical thermal sealing element for effecting a horizontalseal across said plastic film tube and spaced below said fillinglocation and for simultaneously severing said tube to form a toptransverse seal for a filled pouch and a bottom transverse seal for apouch being filled; wherein the multi-layer film comprises an innersealing layer, an outer layer and a core sandwiched therebetween; saidinner sealing layer comprising 40 to 100 weight percent of anethylene/α-olefin copolymer having a density of between 0.902 and 0.912g/cm³, and 0 to 60 weight percent of a polyolefin or a mixture of atleast 2 polyolefins, said outer layer comprising a polyolefin or amixture of at least 2 polyolefins, said core comprising a mixture ofabout 20 to 90 weight percent of a polypropylene, copolymer orterpolymer and about 10 to 80 weight percent of a polyolefin or amixture of at least 2 polyolefins, said multi-layer film structurehaving a thickness within a range between 50 and 70 microns (2.0-2.75mil); wherein the horizontal seal is substantially free of thinningregions.
 2. The method according to claim 1, wherein the polyolefincomprises low density polyethylene, and the mixture of at least 2polyolefins comprises low density polyethylene, linear low densitypolyethylene or very low density polyethylene.
 3. The method accordingto claim 2, wherein the mixture of at least 2 polyolefins in the outerlayer consists essentially of low density polyethylene and very lowdensity polyethylene, and the polypropylene in the core is apolypropylene copolymer.
 4. The method according to claim 1, whereinsaid horizontal sealing jaw has an electrical impulse sealing head whichoperates at a lower temperature due to said thinner multilayer filmresulting in an electrical energy reduction of about 20-40% due to lowermass and lower seal initiation temperature and a corresponding increasein said throughput as compared with a 76 μm (3 mil) mono-layerpolyethylene film.
 5. The method according to claim 4, wherein saidvertical and horizontal seals have a seal integrity resulting in a twoto threefold improvement in drop test performance as compared with said76 μm (3 mil) mono-layer polyethylene film.
 6. The method according toclaim 4, wherein said machine is a milk pouch forming machine having athroughput of one 1.3 liter milk pouch per second or greater per fillinglocation.
 7. The method as claimed in claim 1, wherein the flowablematerial is a liquid.
 8. The method as claimed in claim 1, wherein thecore comprises a polypropylene copolymer having a melting point at least40° C. higher than a melting point of the inner sealing layer.
 9. Themethod as claimed in claim 1, wherein the inner sealing layer has a sealinitiation temperature between about 80 and 95°.
 10. A method offorming, filling and sealing a pouch with a flowable material at highspeed, said method comprising the steps of: i) providing, in roll form,a multi-layer film, said film comprising an inner sealing layer, anouter layer and a core sandwiched therebetween; said inner sealing layercomprising 40 to 100 weight percent to an ethylene/α-olefin copolymerhaving a density of between 0.902 and 0.912 g/cm³, and 0 to 60 weightpercent of a polyolefin or a mixture of at least 2 polyolefins, saidouter layer comprising a polyolefin or a mixture of at least2-polyolefins, said core comprising a mixture of about 20 to 90 weightpercent of a polypropylene, copolymer or terpolymer and about 10 to 80weight percent of a polyolefin or a mixture of at least 2 polyolefins,said multi-layer film structure having a thickness within a rangebetween 50 and 70 microns (2.0-2.75 mil); ii) drawing said film, bydrawing means, over a pouch former to form a plastic film tube having anoverlapped vertical film edge, iii) sealing said overlapped verticaledge with a vertical sealer to form a vertical seal, iv) effecting ahorizontal seal across said plastic film tube with a horizontal sealingjaw and at a predetermined location below said vertical sealer, andsimultaneously severing said tube to form a top horizontal seal for afilled pouch and a bottom horizontal seal for a pouch being filled, saidhorizontal seal being substantially free of thinning regions, and v)continuously feeding a flowable material within said plastic film tubebelow said vertical seal and above said transverse sealing jaw.
 11. Themethod according to claim 10, wherein the polyolefin comprises lowdensity polyethylene, and the mixture of at least 2 polyolefinscomprises low density polyethylene, linear low density polyethylene orvery low density polyethylene.
 12. The method according to claim 10,wherein the mixture of at least 2 polyolefins in the outer layerconsists essentially of low density polyethylene and very low densitypolyethylene, and the polypropylene in the core is a polypropylenecopolymer.
 13. The method according to claim 10, wherein said flowablematerial is milk and said step (iv) is effected at a pouch forming rategreater than one pouch per second for a 1.3 liter pouch per fillinghead.
 14. The method according to claim 10, wherein said top and bottomhorizontal seals have a seal integrity resulting in a two to threefoldimprovement in drop test performance as compared with 76 μm (3 mil)mono-layer polyethylene film.
 15. The method according to claim 10,wherein said horizontal sealing jaw has an electrical impulse sealinghead which operates at a lower temperature due to said thinnermulti-layer film resulting in an electrical energy reduction of 10% andan increase in pouch forming rate of 10% as compared with a 76 microns(3 mil) monolayer polyethylene film.
 16. The method as claimed in claim10, wherein the flowable material is a liquid.
 17. The method as claimedin claim 10, wherein the core comprises a polypropylene copolymer havinga melting point at least 40° C. higher than a melting point of the innersealing layer.
 18. The method as claimed in claim 10, wherein the innersealing layer has a seal initiation temperature between about 80 and95°.